1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly, to a method of manufacturing a semiconductor device with enhancements of its electrical characteristics.
2. Description of the Related Art
With a continuing trend towards large-scale integration of semiconductor devices, the aspect ratio of contact holes has increased. Thus, a tungsten plug is used to ensure good step coverage even when the aspect ratio of a contact hole is more than 2, and to enhance connection capability between a substrate and a first wire.
Generally, a tungsten plug is fabricated in the following manner. First, a barrier layer such as a Ti layer/TiN layer is formed on an insulating layer pattern having a contact hole therein, and a tungsten layer is deposited so that the insulating layer pattern is fully filled. Then, the tungsten layer is planarized so that an upper surface of the insulating layer pattern is exposed to thereby completing the tungsten plug.
In particular, deposition of the tungsten layer is done by reduction of a WF6 gas, which is a tungsten source gas, by a SiH4 gas, which is a silicon source gas, or a H2 gas. At this time, fluorine ions generated by the reduction reaction react with the Ti layer through a pinhole or impurity defect of the TiN layer to generate TiFx gas bubbles. Therefore, the volume of the Ti layer increases to penetrate the TiN layer, which will result in an explosive phenomena (referred to as “volcano defects”, hereinafter) at an angled region of the contact hole such as an inlet of a contact hole or a less dense region of a TiN layer.
In this regard, to prevent penetration of fluorine ions, the thickness of the TiN layer should be sufficiently increased. However, the TiN layer having an increased thickness undesirably has increased contact resistance and a reduced diameter of the contact hole. Therefore, the insulating layer pattern is insufficiently filled by the tungsten layer. In particular, when the TiN layer is thickly sputtered at the entrance of the contact hole, forming a partially projected “overhanging-shape,” it further reduces the diameter of the contact hole.